Most should work with Bulldozer-based Opteron 4200s, since AMD explicitly designed Socket C32 (and its counterpart Socket G34) to specifically work with Bulldozer-based parts. Any of those should be fine. TYAN's dual-chipset board obviously has the most I/O capabilities, but I'd definitely give ASUS the leg over TYAN in reliability and support if something goes wrong. Supermicro would be #1 for customer support, likelihood of new CPU support, and reliability. They also make their boards in the USA instead of Taiwan or China, too.